1. Field of the Invention
The present invention relates to transport mechanisms and, more particularly, to a robot arm transport device.
2. Brief Description of Related Developments
The existing manufacturing technologies for semiconductor integrated circuits (IC) and flat panel displays (FPD) include processing of silicon wafers or glass panels, referred to as substrates, in fully automated vacuum cluster tools. A typical cluster tool is shown in FIG. 1 and may include a circular vacuum chamber with radially connected load locks and process modules arranged in a star pattern.
The tool may be serviced by a robot which is located at the center of the chamber, and cycles the substrates from the load locks through the process modules and back to the load locks. Another robot may be located in an atmospheric transfer module which serves as an interface between the load locks of the vacuum chamber and standardized load ports serviced by an external transportation system.
Typical operations performed by the vacuum robot include rotational and radial straight-line moves in a horizontal plane. In order to position the substrate to a given point in the plane of operation, the robot arm needs to be capable of a planar motion with two degrees of freedom. Since the load locks and process modules, also referred to as robot stations, are connected radially to the chamber, the orientation of an end-effector of the arm needs to be kept radial regardless of the position of the robot arm. Typical arm designs that provide such a functionality include telescoping, scara-type, and frog-leg mechanisms. FIG. 2 shows an exemplary telescoping arm 200a, an exemplary scara arm 200b, and an exemplary frog-leg arm 200c. In many applications, the robot includes a vertical lift drive which provides an additional DOF required to pick/place substrates from/to fixed pins, and for servicing stations at different vertical levels.
The drawbacks of the star configuration of the cluster tool chamber include a relatively large footprint and inconvenient interface geometry. In response to the growing demand for footprint reduction and standardized factory interface, tools with stations arranged in a non-radial manner are being introduced. An example of such an arrangement is the atmospheric transfer module of the cluster tool of FIG. 1. In order to access non-radial (orthogonal) stations properly, the atmospheric robot needs to be capable of moving and positioning the end-effector to a given point with a specified orientation, i.e., providing three degrees of freedom (3DOF) in the plane of operation.
A typical example of such a 3DOF robot may be a planar three-link manipulator comprising an upper arm, forearm and end-effector that are coupled and actuated through revolute joints, as shown in FIG. 3. An alternative four-link design is described in U.S. Pat. No. 5,789,890, issued Aug. 4, 1998, to Genov et al. Typically, the end-effector is driven by a motor located at the robot wrist joint 300a (FIG. 3), or through a multiple-stage belt arrangement from an actuator installed inside the robot arm 300b (FIG. 3) or in the robot base 300c (FIG. 3).
The multiple-stage belt arrangements of 300b and 300c add to the mechanical complexity of the robot arm, present a reliability risk, complicate manufacturing and maintenance of the arm, and produce particles which may leak outside and contaminate the workspace of the robot. The approach of 300a eliminates the drawbacks of multiple belt stages, but the actuator at the wrist joint adds mass to the moving components of the robot, thus limiting the speed of motion and increasing the overall power requirements. In addition, the power and signal lines routed through the moving components of the robot arm often represent significant cost and reliability concerns. This approach is particularly problematic in vacuum applications due to sealing and heat removal issues.